Bioorganic & Medicinal Chemistry Letters
A Casein kinase 1/Checkpoint kinase 1 pyrazolo-pyridine protein
kinase inhibitor as novel activator of the p53 pathway
Anne-Sophie Huart a, Barbara Saxty b, Andy Merritt b, Marta Nekulova c, Stephen Lewis b, Yide Huang d,
Borivoj Vojtesek c, Catherine Kettleborough b, Ted R. Hupp a,
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a p53 Signal Transduction Group, University of Edinburgh Cancer Research Centre in the Institute of Genetics and Molecular Medicine, Crewe Road South,
Edinburgh EH4 2XR, United Kingdom
b Medical Research Council Technology, Mill Hill, London NW7 1AD, United Kingdom
c Regional Centre for Applied Molecular Oncology, Masaryk Memorial Cancer Institute, Brno 656 53, Czech Republic
d College of Life Sciences, Fujian Normal University, Fuzhou, Fujian 350108, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactivation of the wild-type p53 pathway is one key goal aimed at developing targeted therapeutics in
the cancer research field. Although most p53 protein kinases form ‘p53-activating’ signals, there are few
kinases whose action can contribute to the inhibition of p53, as Casein kinase 1 (CK1) and Checkpoint
kinase 1 (CHK1). Here we report on a pyrazolo-pyridine analogue showing activity against both CK1
and CHK1 kinases that lead to p53 pathway stabilisation, thus having pharmacological similarities to
the p53-activator Nutlin-3. These data demonstrate the emerging potential utility of multivalent kinase
inhibitors.
Received 13 June 2013
Revised 7 August 2013
Accepted 9 August 2013
Available online 16 August 2013
Keywords:
Kinase inhibitor
p53 Pathway activation
Casein kinase 1
Ó 2013 Elsevier Ltd. All rights reserved.
Checkpoint kinase 1
Inactivation of p53 tumour suppressor functions is a common
feature of human cancer cells, which has led to extensive drug ther-
apy research focused on targeting specific pathways around p53.1
This inactivation can be achieved genetically by p53 gene mutation
resulting in an attenuation of the tumour suppressor functions of
p53 or by post-translational attenuation of wild-type p53 function
through the over-production of ‘p53-inactivating’ pathways. There
are over four-hundred p53-interacting proteins, many of which
can function as p53-inhibitors, though the clinical relevance of the
vast majority of these protein–protein interactions is undefined.
However, there are a few well-characterised p53 inhibitors that
have been the target of drug development programmes whose leads
can stimulate p53. For example such inhibitory proteins include the
ubiquitin ligase Murine double minute chromosome 2 (MDM2) that
normally mediates p53 protein degradation,2 the histone deacetyl-
ase Sirtuin, whose deacetylation transcriptionally attenuates p53,3
and the protein Casein kinase 1 (CK1) that cooperates with MDM2
to mediate p53 protein degradation.4
key pharmacological feature of Nutlin-3 is its ability to both stabi-
lise p53 protein and destabilise the cell-cycle transcription factor
E2F-1 through disruption of MDM2:p53 and MDM2:E2F-1 pro-
tein-interactions that co-ordinately blocks cell cycle progression.5
In searching for protein kinases that interact with MDM2 and which
are pharmacologically similar to MDM2 as potential drug targets,
we found previously that targeted inhibition of the MDM2-interact-
ing protein CK1 using the ATP-competitive inhibitor of CK1 (D4476)
or targeted CK1a siRNA can, like Nutlin-3, lead to co-ordinated p53
stabilisation and E2F-1 degradation. Indeed the acidic domain of
MDM2 has been shown to be phosphorylated in unstressed condi-
tions by CK1 among others,6,7 which contributes to p53 destabilisa-
tion through increase of MDM2 ability to trigger p53 degradation.8,9
Phosphorylation of MDM2 by CK1 would drive the binding of
MDM2 to E2F-1 and therefore inhibit the ubiquitination of E2F-1
by displacing the E3 ubiquitin ligase SCFSkp2 from E2F-1.10 This pro-
vided evidence that CK1 might form a compelling drug targeting for
coupled activation of p53 and inhibition of E2F-1 that can lead to
cell growth inhibition or death.4
Protein kinases such as CK1 have been described to contribute
directly or indirectly to the inhibition of p53 and surprisingly some
tumour-suppressing p53-activating kinases like Checkpoint kinase
1 (CHK1) and CHK2 can possess oncogenic functions under certain
conditions.11 Therefore, the p53-inhibiting kinases represent novel
targets for anti-cancer therapies. In a similar manner to CK1,
MDM2 mediated degradation of p53 and its druggability forms a
core paradigm for inhibiting protein–protein interactions. Small
molecule cis-imidazole analogues like Nutlin-3 can bind to MDM2
and disrupt its many regulatory protein–protein interactions. A
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Corresponding author. Tel.: +44 1317773538.
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.